Add a room size cap about hubs

[gfodor]

after discussions it sounded like a more conservative value may be beneficial for initial launch. iirc 12 sounded like the most mutually agreed upon value as balancing usefulness vs mitigating concerns about too many people in a room at once.

[gfodor]

Lets do 12. I believe this should be an SFU API enhancement so assigned to you @mquander -- feel free to kick back to me if you believe a client-oriented approach is the right move if the server based approach is too involved. The cap can be a soft cap, we basically just want to make it so if a link is posted to a public internet and is flooded it will eventually converge to not allowing more people in.

[mqp]

This is fine. I'll implement it as a response to the "join" message to Janus.

[netpro2k]

Cool, I can do the client side work for this. @mquander just let me know when its up and what response to expect, then assign the issue to me.

[gfodor]

#208